The present invention relates to a video taperecorder for recording and reproducing a video signal which can easily convert television standards to record and reproduce a desired television standards signal.
The television standards now used in all the countries in the world are not unified, but several kinds of signal modes are used therefor. The typical television standards include three systems of NTSC (National Television System Committee), PAL (Phase Alternation by Line) and SECAM (Sequential a Memoire); some systems in which these typical television standards are slightly modified are also used.
The video signal modes in these three typical television standards are as follows. NTSC is basically in the mode of the interlace scanning of 30 frames/sec (field frequency of 60 Hz), the number of scanning lines per one frame of 525, and the carrier frequency for color signals of about 3.579 MHz. PAL is basically in the mode of the interlace scanning of 25 frames/sec (field frequency of 50 Hz), the number of scanning lines per one frame of 625, and the carrier frequency for color signals of about 4.433 MHz. SECAM is in nearly the same mode as in PAL except the color signal transmission process in which two color difference signals R - Y and B - Y are exchanged for each scanning line, i.e. the chrominance subcarrier is frequency-modulated in a line sequential manner.
Household video tape recorders (VTR's) are usually designed to adapt the television standards in a consumer country. For example, for Japan and U.S.A, adopting NTSC, they are designed so that the rotating frequency of a rotary head is set for 30 Hz which is half the field frequency, one field signal corresponding to 262.5 H's (H: one scanning line) is recorded on one track, and a color signal is recorded in a manner of converting the carrier chrominance signal as a color signal is converted from 3.579 MHz to a low frequency of 629 KHz. Also, for the countries adopting PAL such as West Germany. China, etc. the VTR's are designed so that the rotating frequency of a rotary head is set for 25 Hz, one field signal corresponding to 312.5 H's is recorded on one track, and a color signal is recorded in a manner of converting it from 4.433 MHz to the low frequency of 627 KHz. Moreover, for countries adopting SECAM such as France, the VTR's are designed so that a frequency-modulated color signal is recorded in a manner of converting it into a low frequency or counting down (frequency dividing) it. Additionally, the played-back signal, since the television receivers in each country are adapted to the television standards adopted in the country, is outputted in the signal mode corresponding to that television standards.
It should be noted that VTR's adapting to plural television standards are shipped for areas in Europe where both PAL and SECAM can be received, and for areas where sources of plural television standards are intermingled, such as the Near and Middle East and Southeast Asia.
As described above, since the household VTR's are designed so that they adapt to the television standards adopted in the area concerned, for example, it was impossible to play back, in Japan, the tape recorded in
and also impossible to play back in West Germany the tape recorded in NTSC. Moreover, the VTR's adapted to plural television standards for e.g. the Near and Middle East, can play back the tape recorded in plural television standards; however, the reproduced image involves expansion and contraction to be unsightly, and also the VTR's cannot convert one television standards into another one so as to record the NTSC source in PAL, for example.
Previously known techniques for converting a certain television standards signal into another television standards signal are disclosed in, for example,
(1) K. B. Benson: CBS Television Standard Conversion Technique, J. SMPT, Vol. 70, No. 628 (1961), and
(2) P. Paiger: An all Electronic field-store Television Standards Converter, E. BIU Rev. Part A-Technical, No. 103, p. 90 (1967).
These techniques, however, are embodied in an apparatus constructed in a large scale system; since such an apparatus is expensive and requires a large space, it could be only installed in e.g. a television station. Also, if these techniques are to be used in combination with a television and VTR, troublesome operations of changing the manner of connecting the respective units and setting a new mode were required.
In recent years, there is a growing tendency for information in the world to be unified or centralized and so an eager demand of freely exchanging images among countries. As understood from the above description, the present household VTR's are very insufficient to satisfy such a demand.